This invention relates to liquid sample injecting apparatus suitable for use in performing liquid chromatography, and more particularly to seal means for an outer peripheral surface of a sample needle of the liquid sample injecting apparatus.
A liquid sample injecting apparatus for successively introducing a multiplicity of kinds of liquid samples into a column in performing liquid chromatography is disclosed in U.S. Pat. No. 4,094,195, for example. When liquid chromatography is performed by using this apparatus, the method used comprises a step of drawing a liquid sample into a sample needle, and a step of feeding the liquid sample into the column by using a carrier solvent, the two steps being followed alternately. To this end, the sample needle is constructed such that it moves in sliding movement in an axial direction so that a hole at a forward end portion of the sample needle enters a liquid sample containing vessel to draw the liquid sample when brought to one position, and is then brought into communication with a passageway for the carrier solvent when brought to another position. Advances in the technology for the column have resulted in an increase in the resistance offered by its filter, causing the pressure of the carrier solvent to rise to over 5000 psi. This has raised a problem with regard to a seal around an outer peripheral surface of the sample needle at a connection of the needle with the carrier solvent passageway. The document referred to hereinabove discloses seal means comprising two sleeves formed of fluorocarbon-based material and serving as seal members located on the outer peripheral surface of the sample needle in a manner to hold the carrier solvent passageway between them, and a stress ring having a beveled deforming surface for mechanically compressing the sleeves from opposite sides of the length thereof so as to deform the sleeve radially inwardly to provide a positive seal to the outer peripheral surface of the sample needle. The seal means of this construction is considered to be able to provide a satisfactory seal. However, this seal means would be considered to suffer the following disadvantages. Since the sleeves press against the outer peripheral surface of the sample needle at all times, enhanced resistance would be offered to the sliding movement of the needle, and the service life of the sleeves would be short.